This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to A 1585/99 filed in Austria on Sep. 15. 1999; the entire content of which is hereby incorporated by reference.
The invention pertains to a message transmission system having at least one subscriber""s terminal unit, which is connected, via a subscriber""s line that is constructed of a first and second lead, to a subscribers"" interface circuit (SLIC), preferably integrated, which comprises a loop detector circuit and a subscriber""s feeder circuit, such that in the area of the subscriber""s terminal device, or on it, a subscriber""s signaling display is provided, which may be controlled by means of a signaling control circuit.
Message transmission systems with subscriber signaling displays have been used for some time. In the USA in particular, such subscriber signaling displays are common; with their assistance, a particular condition can be imparted to the subscribers. Thus, the condition xe2x80x9cMessage waitingxe2x80x9d (message ready for retrieval) is displayed by means of low-voltage neon-glow lamps or LEDs that are applied to the subscriber""s terminal unit specifically for that purpose, for which function there exists a need, in hotels, for example, to notify the hotel guests of the existence of a message that has been left at the hotel reception desk in their absence. The message left may be a written notice, for example, or an electronic message (voice message). Customarily, the feeder voltage levels on the subscriber""s line are 24V, 48V, or 60V. In order to prevent, in a manner that is certain, this subscriber""s signaling display from responding at these voltages, the ignition voltage of the low-voltage neon-glow lamps is selected to fall within a range of 90 or 120V, or the LED displays are topped by voltage comparators, which correspond to the LED displays whose threshold limits are adjusted to these higher voltage values. However, these higher voltage levels also presuppose costly discrete SLICs (Subscriber Line Interface Circuits), which have, in contrast to the integrated SLICs, which can be operated with a maximum voltage supply of up to 90V, a correspondingly higher voltage resistance at their disposal, so that they are not destroyed by the relatively high operating voltage of the signaling display lamps. The space needed for this purpose and the expenditure of labor, in terms of circuitry, increase the costs of signaling the subscribers.
It is the task of the invention, therefore, to indicate a circuitry arrangement for a subscriber""s signaling device of the sort alluded to at the outset, a device that can be operated with cost-effective circuits, preferably integrated SLIC circuits.
According to the invention, this is accomplished by virtue of the fact that a controllable switch is wired between the subscriber""s interface circuit and the first lead of the subscriber""s line, a switch which, in a first position, connects the first lead of the subscriber""s circuit and an input of the subscriber""s interface circuit with each other, and in a second position, connects the first subscriber""s line lead with one pole of an additional power source, such that the other pole of additional power source is connected with a feeder voltage input of the subscriber""s interface circuit, and such that the switch that can be controlled via the signaling control circuit.
In this way, the loop detector circuit of the subscriber""s interface circuit can be used, as it has been thus far, to monitor the loop current that flows in the subscriber""s line, such that when the switch that can be controlled is in the reversed state, a subscriber""s signaling display is operated, and if a loop current is detected in one subscriber""s lead, the deactivation of subscriber""s signaling display can be effected. Thus, a separate subscriber""s feed circuit is no longer necessary for the subscriber""s signaling display, as a result of which the need for space and the requisite financial expenditure, when compared with the customary solutions, can be decreased. Furthermore, the expense incurred for separate protection from over-voltage is also dispensed with in the case of the circuit that has been saved.
A variant of the invention can reside in the fact that the additional power source is comprised of a first power source and a second power source that is connected to it in series, such that one of the poles of the first power source exhibits negative polarity, and one of the poles of the second power source exhibits positive polarity, relative to ground potential, and that the negative pole of the first power source is connected to the feeder voltage input of the subscriber""s interface circuit, and the positive pole of the second power source is connected with the first lead of the subscriber""s line in the controllable switch""s second position, such that the extent of the terminal voltage of the first power source does not exceed the maximum allowable operating voltage of the subscriber""s interface circuit.
By these means, the full, maximum voltage can, on the one hand, be applied to the subscriber""s interface circuit with the aid of the first power source, and the difference that is needed to achieve low-voltage neon glow lamp ignition can be provided by the positive second power source, such that positive and negative voltage add up to the requisite ignition voltage.
According to another advantageous embodiment of the invention, the terminal voltage of the first power source can be xe2x88x9285V and the terminal voltage of the second power source can be +40V. Thus, on the one hand, by way of the first power source alone, it is possible to operate a low-voltage neon-glow lamp having a usual ignition voltage of ca. 90V, and, by adding the second power source by means of a controllable switch, it is possible to operate a low-voltage neon-glow lamp having an ignition voltage of ca. 120V.
To safeguard the inputs of the integrated subscriber""s interface circuit against voltage overloads, it is possible, in a manner that is known, per se, to top the latter with an overload circuit, which prevents the destruction of the subscriber""s interface circuit in the event of a voltage overload.
A re-arrangement of the circuitry that can be undertaken in a manner that is safe and sparing in its consumption can be achieved according to an extension of the invention by virtue of the fact that the controllable switch is formed by means of a switching contact of a bistable relay.
Provision can be made, furthermore, for comprising the lead out of the lead to ground because in many instances, two feeder inputs are provided for the other, voltage-bearing lead of the subscriber""s line so that the provision of a higher voltage for the purpose of operating the subscriber""s signaling display can be undertaken, in part, in a very simple manner through the use of these feeder inputs.
According to another embodiment form of the invention, provision can be made so that the circuit with loop detection function that is provided in the subscriber line interface circuit (SLIC), exhibits at least one input for the purpose of detecting the loop current that flows in the first or second lead of the subscriber""s line. In this way, a loop current can be detected even if it flows by way of just one input of the subscriber""s interface circuit. Such an operational case is present if the controllable switch is switched to its second position and thus, the current flow is diverted by way of the additional voltage source. The detection of a loop current is possible, therefore, due to the particular configuration of the subscriber interface circuit, even though the latter flows only into one input of the subscriber""s interface circuit.
For the sake of producing the operational voltage that is necessary to operate the subscriber""s signaling display in a manner that keeps power losses as low as possible, the former can be comprised of a direct current transformer.
Furthermore, according to an additional embodiment of the invention, the direct current transformer can be capable of being controlled in its output voltage, such that one transitional function, preferably in the form of a ramp, between a minimal and maximal value, can be set. With the aid of the transitional function, it is possible to avoid the short-term response, due to a rapid voltage spike, of a ringer assembly that is located within the subscriber""s device. A transition between the turned on and the turned off state that is as continual as possible thus prevents an activation of the ringer assembly.
Furthermore, the invention pertains to a process for controlling a subscriber""s signaling display through the use of a transmission system according to the invention.
The task is to render a switching off of the subscribers signaling display possible with the aid of the subscriber""s interface circuitry, which is provided for the purposes of telephony, in order to save the costs and the space required for an additional subscriber""s feed circuit, including the detectors.
According to the invention, provision is now made so that one pole of the additional power source is connected to the first lead of the participant""s line for the purpose of activating the subscriber""s signaling display and so that the subscriber""s interface circuit monitors the loop current that flows in the second lead of the subscriber""s line, and the subscriber""s signaling display is deactivated when a pre-determined threshold value is exceeded.
In this way, the subscriber""s interface circuit can, on the one hand, perform its functions with respect to feeding, signaling calls and monitoring loop current for the subscriber""s terminal device, and, on the other hand, also provide the signals for the termination of the subscriber""s signaling display as soon as a loop current is detected.
In an additional embodiment of the invention, provision can be made so that the activation and the deactivation of the subscriber""s signaling display is undertaken with a transitional function. The transitional function has, as a consequence, a relatively slow increase in the operational voltage that is necessary for signaling.
For digital controls, it can be advantageous, furthermore, if, by way of extension of the invention, the transitional function is comprised of a ramp-like increase or diminution of the voltage, respectively. In this way, a digital value can be assigned to every voltage step, as a result of which, a programmable control can be undertaken by simple means, whereby, in addition, the transitional function can be embodied, preferably of eight individual voltage steps.
According to a further variant of the invention, provision can be made so that for signaling a call, the controllable switch is placed into the first position, and if a subscriber signaling display is present during pauses in calling, it is placed into the second position.